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Embryology > First Four Weeks of Development > Flashcards

First Four Weeks of Development Flashcards

1
Q

Embryonic Stage (timeline) and characteristics

A

Fertilization to day 56.
Zygote formation, cell division, implantation, organ formation, teratogen sensitivity (environmental agents that could cause congenital abnormalities)

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2
Q

first two weeks

A

TERATOGEN EXPOSURE= minor enough to be okay or spontaneous abortion
no congenital anomalies associated with the first two weeks

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3
Q

significance of weeks 3-8

A

PERIOD OF MAXIMAL SENSITIVITY TO ABNORMAL DEVELOPMENT - malformation of embryo may occur
(something can go wrong post 8 weeks but it would not be considered a malformation)

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4
Q

how long until the female oocyte degenerates? (time for sperm to fertilize)

A

degeneration may occur within 24 hours, however, sperm can last longer within the female
OVULATION OCCURS AT DAY 14-15

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5
Q

zygote

A

the diploid cell formed by the union of the haploid spermatozoa and the haploid ovum - genetically unique cell since half chromosomes from the mother, and half from the father

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6
Q

what is occuring once zygote has formed from fertlization

A

MITOTIC DIVISIONS- called cleavage divisions occuring.
NO INCREASE IN TOTAL CYTOPLASMIC MASS
DAUGHTER CELLS OF THESE DIVISION ARE CALLED BLASTOMERES ciliated cells and peg cells working -

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7
Q

BLASTOMERES

A

daughter cells of the cleavage divisions- mitotic divisions after fertilization - becoming smaller and smaller with each division

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8
Q

morula

A

product of cleavage divisons produced by the blastomers - around 12-24 sources

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9
Q

how long does the zona pellicuda stay in tact?

A

stays intact until about day 19, so about 3 days post-fertilization

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10
Q

when does the first cavity begin to develop in the in the embryo? what is it called?

A

about 4 1/2 to 5 days post fertilization

referred to as the blasoCYST- formed by the blastomere and we have an inner and outer cell mass

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11
Q

what has to happen for implantation to occur?

A

the zona pellucida must be broken down for implantation to occur

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12
Q

window for implantation to occur

A

6-7 days post fertlilization

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13
Q

The two cell layer in the blastocyst

A
  1. Trophoblast

2. Embryoblast

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14
Q

Trophoblast

A

Thin layer around the blastocyst which penetrates the endometrium over the embryonic pole
GIVES RISE TO PLACENTA

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15
Q

Embryoblast

A

INNER CELL MASS OF BLASTOCYST - will give rise to all tissues of the embryo

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16
Q

name of endometrium once implantation has occured

A

decidua

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17
Q

what does the trophoblast proliferate into and describe them

A

two layers

  1. cyrotrophoblast - mitotically active, inner layer of cells
  2. Syncytiotrophoblast- PRODUCES hCG- TO MAINTAIN CORPUS LUTEUM - TO OVARY - MAINTAIN HORMONES UNTIL PLACENTA IS FULLY FUNCTIONING - this is always positioned closest to the maternal blood supply
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18
Q

hCG

A

human chorionic gonadotropin hormone - feedback to the ovary of corpus luteum (hormones maintain the pregnancy until the placenta has fully formed)
Acts on the ovary

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19
Q

day 7-9 post fertilization

A

trophoblastic plate formation and invasion of uterine stroma by blastocyst

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20
Q

two most likely places of an ectopic pregnancy

A

ampulla of the uterine tube and the rectouterine pouch - abdominal cavity

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21
Q

after week one?

A

fertilization and implantation have occured

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22
Q

major events in second week of development?

A
  1. Formation of the bilaminar disc - two layers that arise from the embryoblast or inner cell mass
  2. completion of implantation
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23
Q

embryoblast divides into what two layers

describe them

A
  1. Epiblast which is the dorsal side of the embryo - related to the AMNIOTIC CAVITY
  2. Hypoblast which is the ventral side of the embryo - adjacent to YOLK SAC and called the primitive endoderm and does not contribute to the developing embryo
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24
Q

bilaminar disk

A
  1. epiblast

2. hypoblast

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25
Q

what type of tissue lines all cavities?

A

epithelium

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26
Q

sources of fluid in the amniotic cavity

A
  1. fetal urine
  2. maternal sources - early in development
  3. amniotic cells forming the membrane - small amount
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27
Q

yolk sac

A

cells from hypoblast form a membrane that lines yolk sac
small in humans and contains no yolk
NUTRIENTS LIKE FOLIC ACID VITAMINS A B12 AND E PRIOR TO PLACENTA
aids in primordial germ cells and hematopoiesis
nourished through LACUNAR NETWORKS early in development

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28
Q

primordial uteroplacental circulation

A

provides nutritional needs early in development and is achieved by the trophoblasic lacunae made by the syncytiotrophoblast eroding away to allow maternal blood cells

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29
Q

extra embryonic mesoderm

A

layer that forms betweent he yolk sac and the cytotrophoblast layer
will start to form small cavities and give rise to one larger cavity

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30
Q

chorionic cavity - how is it made and what are its components?

A

result of the extra embryonic mesoderm and divides it into two layers

  1. extraembryonic somatic mesoderm - lining trophoblast and amnion
  2. extraembryonic splanchnic mesoderm- lines yolk sac
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31
Q

components of the placenta

A

Fetal components = what is derived from the chorion (3 components)
Maternal = the decidua - endometrium at sight of implantation

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32
Q

chorionic villi

A

extend outward from the chorion and contact maternal blood through the syncytiotrophoblast

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33
Q

Day 14 in development

A

the embryo has the form of a flat, bilaminar disc, ovoid in shape and in a localized are of the hypoblast, cells thicken and become more columnar and form the PRECHORDAL PLATE

34
Q

prechordal plate

A

at the rostral end of the embryo and indicates the future site of the mouth - close to the oropharyngeal membrane
has a role in the induction of the forebrain and contributes to the mesoderm of the head region

35
Q

end of week two?

A

‘Rule of Two’s’
Embryo is fully implanted
Trophoblast has had a period of growth greater than the embryoblast

36
Q

More detailed description of what has occurred after week two

A

rule of two’s

  1. embryoblast = epiblast and hypoblast
  2. Trophoblast = cytotrophoblast and syncitiotrophoblast
  3. cavities = amnionic and chorionic (3 components)
  4. two yolk sacs - primary and secondary
  5. extraembryonic mesoderm splits into two layers = somatic and splanchnic
37
Q

what do we have at the VERY BEGINNING OF beginning week three of development

A

Bilaminar disc with primitive streak resulting in bilateral symmetry

38
Q

Significant event in the third week of development

A

cell proliferation and migration converts the bilaminar disc to the TRILAMINAR DISC AND GASTRULATION PRODUCES THE THREE GERM LAYERS

39
Q

structures and terms associated with the third week

A

Trilaminar Disc
Gastrulation to produce three germ layers
primitive streak - site of cell migration
primitive node- elevated area at the cephalic end of the primitive streak

40
Q

T/F epiblasts are responsible for making all three germ layers

A

TRUE
Epiblasts migrate through primitive streak and most ventral now is endoderm
mesoderm in middle
then original outer of epi becomes ectoderm

41
Q

cardiogenic mesoderm

A

most cranially migrating cells form the cardiogenic mesoderm and goes ABOVE (cranial) to future position of the oropharyngeal membrane

42
Q

lateral migrating mesoderm during gastrulation

A

paraxial, intermediate, and lateral plate mesoderm

43
Q

day 16

A

will have a difinitive endoderm formed from epiblast cells that replace the entire hypoblast layer

44
Q

what does the endoderm take place of

A

hypoblast layer which has degenerated and now is endoderm formed from migration of epiblast through primitive streak

45
Q

notochord development

A

the ectoderm and endoderm are adhered together at the oropharyngeal and cloacal membranes so the AXIAL mesoderm forms a long cord along the cranial-caudal axis and develops into the NOTOCHORD

46
Q

importance of the notochord

A

SIGNALING CENTER AND INDUCTIVE SIGNALS

  1. vertebral column and base of skull develop AROUND IT
  2. stimulates conversion of overlying surface ectoderm into neural tissue -CNS
  3. transformation of mesodermal cells of the somites into vertebral bodies
47
Q

Adult remnant of notochord

A

nucleus pulposus of the inter-vertebral disc

48
Q

term for zygote as it is migrating through the oviduct

A

morula (during week one around day 3-4)

49
Q

hatching

A

refers to the degeneration of the zona pellucida during week one of the free blastocyst - right before implantation

50
Q

what does the neural tube give rise to?

A

CNS

brain and spinal cord

51
Q

ectoderm derivatives

A

surface ectoderm (many derivatives)
neural plate (neural ectoderm)
neural crest cells
ectodermal placodes

52
Q

columnar epithelial cells of the neural plate

A

neuroectoderm

neuroepithelium

53
Q

what day does the cranial neuropore close (approximately) in humans?

A

day 24

54
Q

what day does the caudalneuropore close (approximately) in humans?

A

day 26 (might not be exact but the caudal pore ALWAYS CLOSES AFTER THE CRANIAL)

55
Q

causation of ectopic spinal nerves?

A

dysfunction in the notochord as it is a signaling center and is crucial in the development and organization of the spinal cord

56
Q

path of neural crest cells

A

as the neural tube is folding, neural crest cells are migrating into the mesenchyme on each side of the tube and go to various locations into neural and non-neural cells
give rise to the cells of the peripheral nervous system as well as other important structures

57
Q

key points of neural crest cells

A
  1. derived from ectoderm related to the neural tube
  2. often called the fourth germ layer
  3. must migrate from their site of origin and undergo ectodermal mesenchymal differentiation
  4. very vulnerable cells
58
Q

what makes neural crest cells so vulnerable

A

must migrate from their site of origin (from ectoderm related to neural tube) and undergo ectodermal to mesenchymal differentiation

59
Q

two types of ectoderm

A
  1. surface ectoderm

2. neural ectoderm

60
Q

Derivatives of surface ectoderm

A

ALOT

- Epidermis, Nails, Hair, Subcutaneous glands, mammary glands, anterior pituitary, enamel, lens of the eye

61
Q

derivatives of neural ectoderm

A

CNS
Retina
Posterior Pituitary gland
Pineal Body

62
Q

intraembryonic mesoderm

A 
mesoderm and its derivateives
the embryonic mesoderm on each side of the neural tube and notochord organizes into three distinct longitudinal columns of cells
1. Paraxial - adjacent to axial
2. Intermediate 
3. Lateral plate mesenchyme
63
Q

paraxial mesoderm

A

next to axial mesoderm
organizes into somitomeres in the head region
from occipital region caudally somitomeres organize into somites
AGE OF EMBRYO IS CORRELATED TO THE NUMBER OF SOMITES

64
Q

What does each somite form?

A

scleretome
myotome
dermatome

65
Q

paraxial mesoderm in the head region?

from occipital region and down?

A

somitomeres

somites (occipital and caudal)

66
Q

scleretome

A

from paraxial somite and forms the axial skeleton or segmental bone

67
Q

dermatome

A

from paraxial somite and forms the epidermis/ dermis/ connective tissue of the back

68
Q

myotome

A

paraxial somite and forms the skeletal muscle of the back, limb, and body wall

69
Q

intermediate mesoderm

A

gives rise to the urogenital system

functionally divided into urinary system and genital system

70
Q

division of the lateral plate mesoderm

A

somatic (parietal) mesoderm

splanchnic (visceral) mesoderm layer

71
Q

somatic/parietal mesoderm

A

this faces the ectoderm and in combination will form the body wall
*in relation to body wall

72
Q

splanchnic (visceral) mesoderm

A

this faces the endoderm and in combination with it will form the gut walls
*in relation to an organ

73
Q

what will the cells lining the parietal and visceral layers of the body cavity differentiate into?

A

specialized simple squamous epithelium called MESOTHELIUM

74
Q

what will the single intraembryonic body cavity give rise to?

A
  1. pleural cavities
  2. pericardial cavities
  3. peritoneal cavity
75
Q

what causes the longitudinal folding of embryo (where is it occuring)?

A

folding due to brain development and causes the head and tail to fold ventrally
on the longitudinal or median plane (cranial - caudal)

76
Q

what causes the lateral fold?

A

due to the growth of the somites

occurs on the horizontal plane (lateral body fold)

77
Q

What week of development is the endoderm (epithelium) folded into the body cavity?

A

fourth week of development

78
Q

What does the endoderm give rise to?

A
  1. epithelium of the gut tube
  2. Liver, gall bladder, pancreas
  3. epithelium of respiratory system
  4. epithelium of SOME of the glands and structures of the head and neck
79
Q

cranial head fold

A

endoderm is incorporated into the embryo and forms the FOREGUT

  • septum transversum
  • primordial heart
  • pericardial cavity
  • oropharyngeal membrane
80
Q

tail folding

A

endoderm lining the yolk sac is incorporated as the hindgut

  • primitive streak
  • cloacal membrane
  • connecting stalk
81
Q

lateral folding

A

GROWTH OF SOMITES
-forms body wall
endoderm is incorporated as the midgut - in communication with the yolk sac

Embryology (7 decks)

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